In recent years, solar cells have been receiving attention as a clean energy source due to the rise in awareness of environmental problems. In general, a solar cell module constituting a solar cell has a configuration in which a transparent front substrate, a sealing material, a solar cell element, a sealing material, and a rear surface protective sheet are laminated sequentially from the photoreception surface side, and has a function of generating electric power by sunlight being incident on the solar cell element.
For example, regarding inks used in solar cell modules and the like, from the viewpoint of design attractiveness, inks the appearance of which is colored with black are required in some cases. As a method of coloring appearance with a dark color, a method of providing an ink containing carbon black is mentioned. However, carbon black absorbs near infrared light to cause an increase in temperature, and thus it cannot be said that, when the ink containing carbon black is used, for example, in solar cell modules and the like, the ink containing carbon black is necessarily preferable.
When the ink containing carbon black is used in a rear surface protective sheet for a solar cell module, the temperature of the solar cell module is increased at the time of using the solar cell module. As a result, the electric power generation efficiency of the solar cell module is decreased.
In this regard, a rear surface protective sheet for a solar cell module has been developed which includes a black resin layer containing an organic pigment such as an oxazine pigment having an infrared-light-transmitting property, a white resin layer having infrared reflectivity, a rear surface protective layer having weather resistance, and the like in order to suppress heat generation in a dark color layer and to cause reflective light to be incident to a solar cell element so that electric power generation efficiency is improved and which is produced by attaching this plurality of layers to each other with an adhesive or the like.
(Patent Document 1).
An infrared-light-transmitting dark color ink containing an oxazine pigment and a curing agent becomes an infrared-light-transmitting dark color ink having high durability of adhesion. (Patent Document 1 [0057]). However, the oxazine pigment transmits light having a wavelength of 700 to 800 nm, and thus the oxazine pigment itself is a pigment having a color close to violet rather than black. For this reason, the infrared-light-transmitting dark color ink in which the oxazine pigment is included in a resin has a color close to violet. Therefore, it cannot be said that the infrared-light-transmitting dark color ink in which the oxazine pigment is included in a resin is necessarily preferable when a black appearance is required from the viewpoint of design attractiveness.
In particular, when the infrared-light-transmitting dark color ink is used in the rear surface protective sheet of the solar cell module, the demand for the electric power generation efficiency of the solar cell module becomes even stronger. The infrared-light-transmitting dark color ink used in the rear surface protective sheet is required to be an infrared-light-transmitting dark color ink which further transmits infrared light. The infrared-light-transmitting dark color ink which transmits infrared light can suppress increases in temperature of the solar cell module by suppressing absorption of near infrared light. In addition, by utilizing infrared light in electric power generation, the electric power generation efficiency of the solar cell module can be further enhanced. Therefore, it is important to use the infrared-light-transmitting dark color ink which further transmits infrared light.
Patent. Document 1: Japanese Unexamined Patent Application, Publication. No, 2012-216689